This invention is concerned with blow molding machines for making plastic articles. It is intended primarily for machines having a table with side faces located at equiangular distances around a center of rotation of the table. For a three station machine, the side faces are at 120.degree. angular relation to one another; and one or more core rods extend from each face.
An injection station is located in position to receive one core rod or group of core rods in an injection mold. Parisons are coated on the core rods in the injection mold by injecting plastic from a plasticizer which supplies the plastic in a molten condition.
A blowing mold is located 120.degree. beyond the injection mold so that while a core rod is receiving a parison in the injection mold, another core rod can be located in a blowing mold at a blow station where the parison is expanded into contact with walls of a mold cavity shaped to the desired shape of the finished product.
At a third station 120.degree. removed from each of the other stations, there is a stripper which ejects blown articles from the core rod so that the core rod is free to return to the injection station to receive another parison.
Such machines can be made with more than three stations so as to include a conditioning station and such other operations as may be desirable, especially the controlling of the temperature of the plastic. The invention will be described as applied to a three-station machine; but application of the invention to other machines will be apparent.
The time that elapses from the closing of the injection mold around a core rod, the injection of the parison, the transfer of the parison to the blowing mold, the blowing and stripping operations and up to the closing of the injection mold again on the same core rod constitutes one cycle of the machine. This invention is concerned with a reduction in the time of the cycle of the machine so that the production of the machine is increased.
In many blow molding machines of the type referred to herein, the length of time that a core rod must remain at the blowing station is usually longer than the time required for injection or the time for stripping. However, the core rods must remain at the injection and stripping stations just as long as at the blowing stations since all of the core rods are connected with the same head and have to move simultaneously.
This invention reduces the length of time required for the blowing operation by cooling the blown article much more quickly so that it becomes stiff enough to be lifted from the blow mold cavity and transferred to the stripping station in a shorter time than with prior art machines.
The invention reduces the time for the blowing operation to such an extent that the injection operation becomes the longest operation in the cycle of the machine and thus prevents the programming of the machine from taking full advantage of the time saved in the long operation.
In order to take full advantage of the shortened blowing operation, this invention also provides, in combination with the more rapid cooling at the blowing station, a plastic pump unit which cooperates with the plasticizer to reduce the time required for the injection of a parison on a core rod at the injection station.
The speed-up in the injection and molding operation introduces another problem in that the core rods are returned to the injection station so often and in such a short period of time that there is not sufficient time for the core rods to cool but another feature of the invention includes a special auxiliary cooler for the core rods and this combination of features at the injection, blowing and stripping stations reduces the time of the blowing machine cycle by approximately 40-60%. It will be evident that this provides a very substantial increase in the production rate of the apparatus.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.